When a transformer core is subjected to a no-load excitation with magnetic fluxes remained through a power-on, a large excitation inrush current flows depending on a loaded phase. It is commonly known that the magnitude of this excitation inrush current becomes several times as much as a rated load current of the transformer. When such a large excitation inrush current flows, the system voltage fluctuates. This may affect a user when the voltage fluctuation is large.
Conventionally, the following various methods for suppressing the excitation inrush current are known.
(1) Connect a breaker with a resistor having the loaded resistor and a contact connected in series to a breaker main contact in parallel to load the breaker with the resistor prior to the breaker main contact.
(2) Load an arbitrary phase in advance when a three-phase transformer of a direct-grounding system is loaded with three single-phase breakers, and then load. the remaining two phases.
(3) Load arbitrary two phases in advance when a three-phase transformer of a non-effective grounding system is loaded with three single-phase breakers, and then load the remaining one phase.
(4) Use a three-phase batch-operation type breaker having a single operation mechanism that performs loading and an opening operation simultaneously on a three-phase breaker.